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AFE4960EVM: Difference in Data Between ECG Channel 1 and Channel 2 in AFE4960 2-Channel ECG Configuration

Dhivin Chacko
Prodigy 35 points
Part Number: AFE4960EVM
Other Parts Discussed in Thread: AFE4960

Tool/software:

Hi,

I’m working on a 2-channel ECG configuration with the AFE4960, and I’ve noticed that the data from ECG Channel 1 and ECG Channel 2 differ when I plot them. Specifically:

Channel 1 values are in the negative region.
Channel 2 values are in the positive region.


I was under the impression that these values would be similar or the same. Could someone clarify if this is expected behavior, or if there might be something wrong in my configuration?

Thanks

  • 0
    TI__Guru 63906 points

    Hi Dhivin,

    Thank you for your post.

    How much of a discrepancy are you seeing? It's possible for there to be some difference in offset voltage. These ADCs use binary two's complement to represent the bipolar input range. Are your test signals coming from a live subject or a patient simulator? Is an RLD electrode used to bias the signals?

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 35 points

    Hi,

    Thanks for the response.

    Please see the attached GUI plot of ECG 1 and ECG 2 showing a difference in amplitude

    The test signals were taken from an ECG simulator, with the following connections to the AFE EVM board:

    LA to EX1
    RA to EX2
    LL to EX3
    RL to EX4

    AFE GUI Plot.pdf

  • 0 in reply to Dhivin Chacko
    TI__Guru 63906 points

    Hi Dhivin,

    This looks to be just a difference in offset between the channels, which can arise from several factors, include contact quality, differences in trace routing, and channel-to-channel variation, and possibly the simulator itself. I do not see anything wrong with the configuration.

    Regards,

    Ryan

  • +1 in reply to Ryan Andrews
    Prodigy 35 points

    Hi Ryan,

    I have double-checked the connections, and everything looks good.

    Initially, since I am using only the AFE1 chip, I shorted the jumpers on J1 only as shown.

    Later, I also shorted pins 15 and 16 on J2 (AFE2_RX_SUP to RX_SUP), and after that, I observed a significant improvement in the signal from the 2-channel mode as shown below

    Do you have any insight into how this short improved the signal?

  • 0 in reply to Dhivin Chacko
    TI__Guru 63906 points

    Hi Dhivin,

    Since the electrode inputs are shared between the two AFEs, it may be that AFE2 was passively loading the electrode inputs while left unpowered. I think for your evaluation of one AFE4960, it is ok to leave both powered for now. Otherwise, you can try uninstalling the 0 ohm resistors which connect the electrode signal path to AFE2:

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 35 points

    Hi Ryan,

    Thanks for the information

    The waveforms for Channel 1 and Channel 2 are still showing some offset and are not fully overlapping.

    Is this acceptable, or is further adjustment needed?

    What steps should be taken to align the two channels and make them identical?

  • 0 in reply to Dhivin Chacko
    TI__Guru 63906 points

    Hi Dhivin,

    The waveforms look acceptable. You are testing two different ECG leads (Lead I and Lead II), so I would not expect the outputs to be identical. The offset voltages of each channel are much improved from the previous test and both are within an acceptable range.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 35 points

    Hi Ryan,

    Thank you for the support

    Regards,

    Dhivin